Using UnsafeAlignedOffset to make the entire record of 8 byte Items aligned like which is used in UnsafeExternalSorter

Details

Description

The class of UnsafeExternalSorter used UnsafeAlignedOffset to make the entire record of 8 byte Items aligned, but ShuffleExternalSorter not.
The SPARC platform requires this because using a 4 byte Int for record lengths causes the entire record of 8 byte Items to become misaligned by 4 bytes. Using a 8 byte long for record length keeps things 8 byte aligned.